As codified in Mishna B'rura 592 and elsewhere, we allow someone who has already fulfilled a mitzva to exempt another in the b'racha recited for it — though we try to avoid it where feasible. For example, someone who has read or heard the m'gila (Ester) already can recite the b'rachos over the m'gila for someone else about to hear the m'gila, though we prefer the latter recite them instead. The same is true [citation needed] for a b'racha which is a mitzva, such as kidush l'vana.

Suppose someone, call him R'uven, is unsure whether he's fulfilled his obligation, say of reading m'gila or saying kidush l'vana. Then common practice is that he not recite the b'rachos himself but listen to another who is surely still obligated and fulfill his obligation that way. Now suppose Shim'on is also unsure whether he's fulfilled his obligation (and his doubt is independent of R'uven's). Consider: There's uncertainty about R'uven's obligation to recite the b'racha, and there's uncertainty about Shim'on's; there's a double uncertainty (s'fek s'feka) whether both are not obligated to recite the b'racha, so we should be able to assume at least one is obligated. In that case, one of them should be able to recite the b'racha for the both of them, in accordance with the principle outlined in my first paragraph. (This, assuming there's no one around who is surely obligated and can say the b'racha for R'uven and Shim'on.)

I wonder whether there's anything wrong with that argument, and whether any pos'kim have used or rejected it.

  • I wonder why you are asking this during Sefirat HaOmer...
    – Double AA
    Commented May 12, 2014 at 13:12
  • @DoubleAA, the truth is, this is not so relevant to s'fira, because we hold any safek (not just a s'fek s'feka) whether you counted allows you to continue s'fira with a b'racha. (But CYLOR.) But, yes, s'fira brought this question to mind.
    – msh210
    Commented May 12, 2014 at 14:36
  • Adderabba. We hold you need a s'fek s'feka as well, just the first safek is very easy to come by. Meaning if you have some other safek, it's very easy to find a friend to be your other safek.
    – Double AA
    Commented May 12, 2014 at 15:36
  • Quite right, @DoubleAA.
    – msh210
    Commented May 12, 2014 at 15:53
  • Your initial assumptions are « R'uven, is unsure whether he's fulfilled his obligation » and « Shim'on is also unsure whether he's fulfilled his obligation » and then after your discussion you say « so we should be able to assume at least one is obligated ». IMHO the discussion does not change the initial assumptions. Both are unsure – neither is obligated! Commented May 12, 2014 at 16:44

2 Answers 2


Although in Hilchos Sefiras Ha'Omer we find that one makes a bracha based on a sfek sfaka (Mishne Berura 489:38), in general one may not rely on a sfek sfakah to make a bracha (Mishne Berura 215:20).

Rav S.Z. Auerbach (Halichos Shlomo, Pesach 11, note 24) explains that with Sefiras Ha'Omer nearly all Poskim agree that one makes a bracha even if he forgot to count one day (disagreeing with the opinion of B'Hag). Therefore, in that case we permit the recitation of a bracha with a sfek sfaika)

Whether someone who may have forgotten to count one day may be motzi another who always counted there is some disagreement among Poskim if, according to B'Hag) he is considered hayyav in the mitzva but technically can't count (Bais Halevi cited in Har Tzvi 2:25) and therefore can make the bracha for someone else, or is not hayyav in the mitzva since he missed a day (Kaf Hachaim 489:91) and can't be motzi another.

See Dirshu Mishne Berurah (ibid) for more details.


A can make a bracha for B's mitzva from the law of erivus - Guarantor - the fact that you have not done a mitzva is my problem, and I am obligated in your mitzva.

ערוך השולחן אורח חיים סימן רעג קיי"ל דכל המצות יכול אדם להוציא אחרים אף על פי שהוא כבר יצא או שהוא לא יצא עדיין ולא דמי לברכת הנהנין שאינו יכול להוציא אחרים אא"כ גם הוא נהנה עמהם דמצוה שאני דכיון דעל השומעים מוטל חובת המצוה לקיים כל ישראל ערבים זה בזה ומוציא אחד את חבירו

As above - this is for obligations, and not for example food where you are not obligated to eat.

Your case is not a s'fek s'feka. There is one sofek. Is B still obligated in his mitzva. It does not matter if A is or not, as Bs obligation falls on A if B has one. And it does not fall on A if B does not.

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